text:
What is the direction of the sideslip induced by roll on a conventional aircraft?
For the sake of this question let's assume that the considered aircraft is an A320. The question is what is the sign of the aerodynamic $C_{n_q}$ coefficient? In another word, when the aircraft starts rolling, will the aircraft experience sideslip and if yes in which direction (and most of all why) ?
Instinctively, I would say that if the right wing (seen from behind) goes down (positive roll rate), it will be delayed compared to the left one, however I already read somewhere that the coefficient tends to be zero (no sideslip induced). I even heard some aeronautical engineers say that it is the opposite...
If needed, we can set that the x-axis is pointing backward and z down.

How do you end up with x-axis pointing backward, but positive roll meaning right wing down. That is pretty non-standard in my experience as it conflicts with the right hand rule. Also you don't define the direction of your y axis, which is pretty essential if you want to discuss the sign of the $C_{n_q}$ coefficient. And since you define the direction of p non-standard, do I need to assume q is also non-standard?

Please add a list of symbols and definition of you axis frame of reference, include signs of rotations. For me, the letters you use don't correspond with the description you give.

You did not say what causes the roll. If the aircraft is thrown around by a gust you will not see adverse yaw. In case of hitting an updraft unsymmetrically, the uplifted wing is pulled forward by the updraft. If the pilot commands the roll, adverse yaw (means opposite to what is needed in a coordinated turn) will result. And, please, no capital cs for the coefficients!

To answer what you wrote: $c_{n_q}$ is the yawing moment induced by a pitching motion. In a conventional, symmetric configuration this is zero for the airframe and has a small value for propeller aircraft, depending on the rotation direction of the propeller. If the tractor propeller is spinning clockwise (when seen by the pilot), a positive pitch motion $q$ (nose up) will cause a small negative sideslip angle $\beta$. A positive pitch acceleration will add a precession moment which similarly pulls the aircraft's nose to the right. But I think you want to know something else.
To answer what you meant: $c_{n_p}$ is the yawing moment induced by a rolling motion. The axis system you propose (with z pointing up) is used to measure relative positions within the airframe, but for flight mechanics we prefer to put the x-axis in flight direction, y to the right and z down. A positive rolling motion $p = \omega_x\cdot\frac{b}{2\cdot v_{\infty}}$ (or $p = \omega_x\cdot\frac{b}{v_{\infty}}$, both definitions are used) is right-wing-down, and a positive yawing moment means the aircraft's nose moves to the right, causing negative side slip angles.
When a positive rolling motion happens in still air, the resulting yawing moment is negative, pulling the aircraft's nose left, as Federico said. Thus, $c_{n_p}$ is negative.
But the reason is different: When the pilot deflects the ailerons and causes a difference in lift on the left and right wings, and consequently a difference in induced drag, the yawing moment caused by that difference in induced drag is called $c_{n_\xi}$, the yawing moment due to aileron deflection. $c_{n_\xi}$ is positive.
Once the aircraft is in a steady roll, the roll damping $c_{l_p}$ will fully compensate the differential lift caused by aileron deflection. Now the rolling motion will increase the local angle of attack on the downward moving wing the farther you are away from the center, and decrease it on the upward moving wing. Since lift is perpendicular to local airflow, the air force vector on the downward moving wing is pointing slightly forward, and that on the upward moving wing slightly backwards. Please note that the total lift produced by each wing is roughly the same! The rolling moment of both is exactly zero once the roll rate is steady. However, the aileron deflection will decrease lift on the downward moving wing such that it just compensates for the increased angle of attack due to the rolling motion, and the same holds for the upward moving wing with its trailing-edge-down aileron deflection.
What is different is not the magnitude, but the direction of lift on both wings. This pulls the downward-moving wing forward and the upward moving wing back, causing a negative yawing moment in a positive rolling motion. That is why your conventional $c_{n_p}$ is negative.

First, a clarification. The standard reference frame for and aircraft, w.r.t. a person sitting in the pilot seat, is:

x axis positive ahead of the aircraft
y axis positive in the right wing direction
z axis positive towards down

In addition, to be clear about the conventions used in the rest of this answer:

positive roll is when the right wing is down
positive sideslip $\beta$ is when the pilot sees the air coming from the right side.

And, for completeness, $C_{N_p}$ is the aerodynamic derivative of yaw rate $r$ (not $\beta$) as function of roll rate $p$.
While $C_{N_q}$ would be the one due to pitch rate $q$, but that would not be within your specified range of conventional aircraft.

Now to your question.

when the aircraft starts rolling, will the aircraft experience sideslip and if yes in which direction (and most of all why) ?

TL;DR version:
Yes, it experiences sidelip and for positive roll rate $p$ the sideslip $\beta$ will be negative.
Extended version:

Positive roll rate means that the right wing is rotating down and the left wing up.
This translates in a momentarily higher Angle of Attack $\alpha$ seen by the right wing w.r.t. the left wing
Because of this difference in $\alpha$ seen by the wings, the right wing will produce slightly more lift (and this is the direct cause of the Roll Subsidance)
Nevertheless, aileron deflection will make the left wing produce significantly more lift
More lift means more induced drag
More induced drag means that the left wing will tend to "lag" and the left wing will move ahead.
The plane has thus rotated towards the left side, achieving a negative $\beta$

The amount of $\beta$ will obviously depend on the specific aircraft.
You might find more by looking for information about the Dutch Roll.

I think you’re right all the way up to induced drag part. Here I think you got it reversed. Even though there is slight lift difference between two wings due to different local AOAs, the bigger chunk of lift difference comes from aileron deflection. That surpasses the former. Therefore left wing will have larger induced drag than right wing. And this will cause left yawing motion in a right roll in a conventional aircraft, which we call adverse yaw. The way you described it sounds like proverse yaw.

@Kolom I think you might be right, I'll revise

Instinctively, I would say that if the right wing (seen from behind)
  goes down (...), it will be delayed compared to the
  left one

You are correct.
This answer is aimed at the case where the ailerons are centered, and the local airmass is uniform, and the aircraft is rolling for some unknown reason (such as retained rotational inertia in the roll axis from a previous disturbance.)
The right wing will experience an increased angle-of-attack due to the rolling motion, and thus will experience more drag.
If we are talking about a steady-state rolling motion (constant roll rate) due to deflected ailerons, then the exact opposite is true -- see https://www.av8n.com/how/htm/yaw.html#sec-adverse-yaw for more.
Likewise if an updraft is striking the rising wing and causing the rolling motion.

authors: Василий Дубов


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Why are some airplane wings not painted?
Why is it that some wings are not painted on commercial jets? Couldn't they paint them the same color as the fuselage or would it be a waste of money?

Almost every aircraft wing I've ever seen was painted. They're just usually painted white.

Related: Why are planes generally pained white?

Airbus requires paint on all surfaces, including the wing. Usually, Airbus wings are painted light grey.

Painting robots at Boeing, Airbus decorated wings.

A number of aircraft manufacturers do paint the wings; only that the color is more neutral (like white or gray) rather than the flashy aircraft liveries as found in the fuselage and vertical tail. According to Boeing, the wings are indeed painted:

Wing skins are made of bare aluminum and are protected by an impact-resistant paint system.

Modern wings are composite and are protected by paint anyway:

Protective paint is used in certain areas to prevent corrosion, and it is used on all composites to prevent erosion and moisture ingress.

It appears that the wings of Airbus aircraft are also painted:

... operate within the Airbus UK wing production facility, painting all narrow-body wing sets.

As for painting in airline livery, it would add another coat of paint, adding weight (For example, paint in A380 weighs half a ton already). Not a lot of people is going to see the wing paint anyway.

Fuselage present a large vertical surface with greater length than height. Wings are a large horizontal surface that is shorter in the direction of travel. So...
The fuselage paint job is clearly visible on the ground, painting on the wings only if you are above or below the plane. This is probably the main reason. Simple geometry. It would be waste of money.
Sun will heat a large horizontal surface more than a large vertical surface, so making the wings white is more useful than making the fuselage white. While I am not sure that wings would be structurally weaker if heated, the heat would cause thermal expansion, which would indirectly result in increased drag by making maintaining optimal shape more difficult.
Paint has significant effect on drag, more specifically it affects when the boundary layer transitions from laminar to turbulent. In the very long fuselage the difference is probably insignificant and you can paint them as you wish, but for wings the paint should be as smooth as you can make it. While I doubt white paint is smoother than paint of any other color, keeping it simple is probably a good idea.

"...but for wings the paint should be as smooth as you can make it".  You may want to double-check that with physics and aerodynamics experts.  I've heard that if you make it too smooth, it can add drag due to the complexities of physics that are beyond my knowledge.

@RockPaperLizard I think I can guess what that is about, and if so, it shouldn't normally be an issue on commercial jet liners.

American Airlines didn't paint many of their older aircraft, leaving them mostly bare metal, to save weight and thus fuel. However, their newer aircraft are painted because it's required to protect composites.
Regarding colors of paint, most planes are mostly white because it absorbs the least heat, doesn't fade and makes leaking fluids or corrosion more obvious. Any other colors used are typically the minimum required for branding.

In some military aircraft, like the P-51 Mustang, the wings were often not painted. This is because the rough camouflage paint made the P-51 Mustang go about 8 miles slower. I don't know if this is the same reason for commercial planes, but it was for the P-51 Mustang and other military planes.
Many commercial planes actually do have paint on the wings, but the paint is white, or light grey.

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Are there countries where commercial flying can be conducted with a Mexican DGAC private pilot license?
I have a Mexican DGAC licence. Can I work in other countries, or do I need to get another licence? (for example an FAA one if I want to work in the US)

Which country's DGAC do you mean (there are several)? We have a lot of questions about using a license from one country in another one, this one might be relevant for you.

Mexico. I guess you get it the same way as if you had a EASA Licence so thanks!

In the US you can do certain commercial flying, such as glider towing, with an FAA license, but I don't believe you could with your Mexican license.

No. If you want to make commercial activities, you need a commercial license.
I remind you the definition of commercial flight

This is not strictly true under FAA regulations. In the US, with an FAA private pilot certificate, certain commercial flying is authorized, for example glider towing.

@JWalters Glider towing is not defined as commercial flight!

The question you linked to isn't really relevant here: it's about how the CBP defines commercial flight, not how the FAA defines it.

@Pondlife it is an ICAO definition. It is the same worldwide.

That's good to know, I didn't realize it was an ICAO definition!

The FAA defines commercial flying as flying for compensation or hire, to potentially include towing gliders. I can point you to the pertinent LOIs if you need more convincing.

@JWalters yes, please.

See Martindell (2009) and MacKenzie (2009). The FAA defines commercial flying, in pertinent part, as: "any nonmilitary flying as a required crewmember [...] for which the crewmember is paid for his or her services." See also 14 CFR 61.113(g): A private pilot [...] may act as a pilot in command of an aircraft towing a glider or unpowered ultralight vehicle. See also Umphres (2010): "§61.113(g) permits a private pilot to act as PIC for compensation or hire of an aircraft towing a glider".

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text:
Can the Safety Pilot log an approach if acting as PIC?
Suppose you are acting as Safety Pilot and PIC on a flight in IMC. Further suppose that the pilot at the controls is instrument rated but his or her IFR currency has expired. If the other pilot acts as sole manipulator of the controls during an approach, can you, as the PIC, log that approach as well? Assume the approach is loggable given weather conditions, etc.

When asking about regulations, always specify the relevant jurisdiction, either in the question text or using an appropriate tag. You can [Edit] your question.

If you aren't current then you probably can't log the time at all, the safety pilot is PIC.

Welcome to Aviation.SE!

Welcome to aviation.SE! Can you clarify a couple of details? First, are you asking about US/FAA regulations? Second, at least in the US there's no such thing as a safety pilot in IMC; did you mean that the flight is in VMC but under IFR?

@StringForever What sort of details, beyond jurisdiction, would improve this question?

@PondlifeI I don't believe that is true: a safety pilot is required anytime the pilot flying is wearing a view limiting device, regardless of meteorological conditions at a particular moment.

@JWalters 91.109 says "No person may operate a civil aircraft in simulated instrument flight unless [...]" They key word is "simulated": in actual instrument flight the concept of a safety pilot doesn't apply. See this answer, which quotes an FAA legal interpretation. Unfortunately the FAA managed to break their website again so I don't have a direct link to hand.

@JWalters This answer might be clearer

@Pondlife Walker (2011) that you reference does not specify a safety pilot in a situation where a view limiting device is used to simulate actual meteorological conditions, but in IMC. If, however, a view limiting device were used the safety pilot would still be required. Note that IMC and loggable instrument time are different things; a pilot might  be flying in IMC but not in loggable instrument conditions. A safety pilot is required anytime a view limiting device is used. In this scenario, however, this issue is immaterial since the answer is no, only the PF/SMOTC may log the approach.

Let us continue this discussion in chat.

No, a pilot may not log an approach that he or she did not perform as the sole manipulator of the controls.
According to the FAA, in order for a pilot to have performed a loggable approach, that pilot must have performed that approach as the sole manipulator of the controls. A required SIC may not log an approach that the PIC flew, nor may a PIC log an approach that was flown by the SIC. Likewise, a safety pilot, though he or she may be a required crewmember for a flight, may not log an approach that was performed by the other pilot.
This hinges on the FAA considering the word "performed" in 14 CFR 61.57 (c) to mean fly the approach as the sole manipulator of the controls. See the FAA's leter of interpretation Carpenter (1999) which addresses this issue:

As the SIC you have not "performed" the approach as contemplated by FAR 61.57(c) because you were not the sole manipulator of the controls during the approach.

But, can the SMOTC log it either if he's not current?

Yes, a non-current pilot can log an approach flown under simulated instrument conditions or under actual conditions with an appropriately rated and current PIC. For example, a pilot who's currency lapsed 4 months prior may fly with a current PIC, perform and log the appropriate number of approaches, and thereby return to currency.


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Am I expected to stay on glide slope for landing in a light aircraft?
When I land the airplane (Cessna 172, 182, 152) I notice that I come in pretty far above glide slope (four white lights on the PAPI).  I pick an aiming spot on the runway (like the second center line stripe) and maintain my approach airspeed while flying towards that point.  I'm able to reach that aiming point with quite good accuracy and land the plane smoothly and softly, but I'm above glide slope for most of the approach, and then on short final the white lights start to turn red.  Clearly my approach is steeper than the usual 3 degree glide slope.  I thought that's what flaps were for - to allow for a steeper approach.  Am I doing this wrong?  Should I focus on staying on glide slope, or should I focus on my aiming point?  I've had several flight instructors and most of them have never said anything about this.  I kinda like being a little higher, and approaching exactly on glide slope usually means I have to add power on short final because I start getting too low.

How long is the runway you're landing on?  When I was based at a field with 10,000+ ft runways, I found it useful (in a Cherokee) to touch down a couple of thousand feet beyond the official markings, because it meant I'd be at the right speed to turn off at the taxiway, instead of having to taxi down the active runway.  IMHO, you should focus on being able to control the plane in order to do what you want to do.  That is, you should be able to stay on that glideslope, and you should be able to make a steeper approach.

Remember, glidepath guidance has its apex or ending point centered on the official precision landing markings (what most people call the thousand footers). This is officially called the aimpoint or aiming point. Large aircraft do not have much float when flaring. They both aim and touch down near the same point. Walk out to a point abeam the thousand footers. You will see the vertical guidance equipment located next to the runway, beside the thousand footer markings.
Your little Cessna floats so much that your aiming point and your touchdown point are not coincident. If you want to land on the thousand footers, you have to aim at the first touchdown marking (the five hundred footers). If you follow the VASI, PAPI, ILS or RNAV glideslope/glidepath all the way down to the ground, you will float past the thousand footers as soon as you enter ground effect.
You are supposed to stay above the glideslope to provide for obstacle clearance all the way to a point where landing is assured. This is usually either the runway lead up lights (MALSR, ALSF, etc) or the runway threshold. Most instrument approaches will include a Threshold Crossing Height on their charts.
During training, focus on landing based on sight picture alone. You will need that when landing on runways without vertical guidance. There are a lot of them. You will also need that skill when doing actual, non-simulated short field and soft field landings. On a real short field landing with a 50 foot obstacle, your aiming point Will be well before the Arrival End of the Runway. It may even be before any concrete starts.

Err... Did you mean "runways withOUT vertical guidance"?

@jamesqf - Yes, without vertical guidance.

I disagree with you about aircraft floating. Having extensive experience flying single engine Cessnas and jet transport category aircraft, and observing the latter, the larger aircraft tend to float further. Float is a function of multiple factors, all controllable, speed being on of the primary factors.

Many glidepath guidance systems are also not coincident with the precision runway aiming point markers.

@JWalters - You are right. Float is a function of many contributing factors. Airspeed, wing design, and rate of pitch change being some of them. The point is that float is a phenomenon that must be accounted for. There will be some deviation from the glideslope after the aircraft is in a position that landing is assured. As far as vertical guidance systems not always being coincident with their expected angle and positions, that is also true. In many cases, this is noted on charts because it is different than the expected.

Well, GP/VGSI non-coincidence is noted. GP non-coincidence with precision aiming point is not directly noted; this can be deduced from TCH and GP angle.

Your newly added point about aiming point on short field over obstacles does not seem right. I used to fly 206 and 185 in the backcountry of ID and WA, and aiming point for these short field landings was always within the landing surface area, never short of it. True short field technique involves precisely holding a minimal approach speed and flaring toward a stall with little or no float.

It is more important that your approach is stabilized and safe than you are strictly on slope (i.e. two red/two white). But let's discuss a few things before extending this answer.
ATC is not terribly concerned with where exactly you touch down (especially in a light aircraft) so long as you don't run off the end of the runway. When cleared to land the whole length of the runway is yours to work with:

If receiving “cleared to land” instructions from ATC, you are
authorized to use the entire landing length of the runway and should
disregard any LAHSO holding position markings located on the runway.
If you receive and accept LAHSO instructions, you must stop short of
the intersecting runway prior to the LAHSO signs and markings.

Different runways will call for different touchdown situations which is why it's important in preflight to understand what your landing distance and roll out will be.
In any aircraft you fly you should be proficient (or learning to be proficient) in various landing techniques than includes standard approaches as well as no flap approaches and short field landing maneuvers. If you have all these things in your toolkit you will be fine. If you are proficient in an aircraft you should be able to put it down on the numbers or the 1000 foot markers or any other spot your instructor asks you to demonstrate so long as there is sufficient distance to roll out and stop. You should focus on being able to deliberately put the aircraft down on a spot of your choosing rather than thinking of it in terms of "i always end up touching down on the mid point of the runway" as the latter statement means a very different thing on a 2000 ft runway than it does on a 10,000ft runway. This can generally be controlled with small pitch and power changes on final.
Generally speaking you should fly the glide path if it is available to you as this will guarantee obstacle clearance and keep you safe. While it is never bad to be a bit above glide path (three white, one red) it can be problematic to be very high (all white). The issue with 4 white lights on a PAPI is there is no further indication of how far above glide path you actually are. Making the assumption that you are anywhere near the glide path if you see 4 white lights is dangerous and can lead to a fast, unstable, slam dunk approach. Slope adjustments can be a bit delayed on approach and a power increase will generally bring you back up to slope if you are low while chopping the power will bring you down to slope but remember it will take some time to settle in so you need to think ahead of the airplane.
If you put it all together you will see that staying on slope brings you down to the 1000 'footers, keeps you clear of obstacles, and allows you to make small final adjustments to control your touch down if you want to land a bit short or a bit long.
It is not a question of focusing on one OR the other but focusing on both and realizing how they play together. If you come in on slope you can make small power changes to adjust your aiming point and suit your desired maneuver.
The FAA's Approach And Landing Chapter of the Airplane Flying Handbook has lots of good info on the matter and is worth the read.

Stabilized Approach Concept
A stabilized approach is one in which the pilot establishes and maintains a constant angle glide path
towards a predetermined point on the landing runway. It is based on
the pilot’s judgment of certain visual clues and depends on the
maintenance of a constant final descent airspeed and configuration.
An airplane descending on final approach at a constant rate and
airspeed is traveling in a straight line toward a spot on the ground
ahead. This spot is not the spot on which the airplane touches down
because some float occurs during the round out (flare). [Figure 8-9]
Neither is it the spot toward which the airplane’s nose is pointed
because the airplane is flying at a fairly high AOA, and the component
of lift exerted parallel to the Earth’s surface by the wings tends to
carry the airplane forward horizontally.

To address some points of your directly:

I thought that's what flaps were for - to allow for a steeper approach.

Flaps allow you to fly a steeper decent angle at a given airspeed, this is not a blanket security measure to fly arbitrarily steep approaches at 80Kts in a 172. They also help you to generate more lift at a given airspeed so you can fly a standard approach at a slower than normal speed (think short field landing).

...and approaching exactly on glide
slope usually means I have to add power on short final because I start
getting too low.

If you are on glide slope on short final you are not too low (thats the point of a glide slope). If you are high for most of the approach, cross the slope, then find your self sinking below slope your approach is not stabilized and you are likely coming in hot then cutting power and diving for the runway.

I kinda like being a little higher

While there is no strict regulation on flying above glide slope flying arbitrarily high is typically an indication of an unstable approach that will result in a slam dunk dive final. The glide slope exists for many reasons and should be followed for those reasons.
If you are student pilot (you dont mention here) work on flying stable, on slope approaches. If you already have your ticket I would start some Instrument training and understand what its like to fly the slope in the soup (or foggles) and how being high can be a real issue when you break out, it might help put it all into perspective.

The slam dunk can be a useful skill to have in specific situations, but it certainly shouldn’t be normal.

Flaps generate more lift at the expense of more drag. Their primary purpose is to allow you to fly slower, with the side effect of letting you descend more steeply without gaining speed.
Your default should always be to use the VSGI when one is available, and to try to stay on glide slope, unless you are deliberately doing something unusual like a short field landing, power off 180, etc. This will build good habits and control that is critical when you advance to instrument flying and larger aircraft.
I can't say for certain why your instructors haven't commented on your steep approaches; maybe they just didn't care since it was "working" for you. I'm sure they would have said something if you were consistently below glide slope, though.
If you're flying your pattern with the appropriate flap settings, speeds and distance from the field, you shouldn't have much trouble staying on glide path. Without seeing you firsthand, I'd guess that you're too high or too fast, which makes you reduce power too much and dive toward the runway, and then on short final you need to add more power to shallow your dive. If you were on glide path to begin with, you would be reducing power on short final since you're about to enter ground effect.

Regarding the 172, and any other single engine aircraft, a better question might be:

what if I lose my engine on final approach?

We can start by looking at the angle and rate of descent with no power at Vbg, around 65 knots.  With an 8:1 glide ratio, no flaps, the angle of descent is:

arc sine (1/8) = 7.2 degrees
rate of descent = 65 knots × 1/8 × 6076 feet/nmile ÷ 60 minutes/hr = 823 feet/minute

We can see that, if local regulations allowed, a higher angle of approach would be the safer way to assure reaching the runway, particularly if there were obstacles such as buildings or power lines in the flight path.
At a low idle:

thrust is proportional to rpm$^2$

 thrust required for level flight @ 65 knots= Weight × .125 = around 300 lbs or roughly 1700 rpm
900$^2$/1700$^2$ × 300 lbs = 84 lbs of thrust

Angle of descent at idle = 7.2 × (300-84)/300 = around 5.2 degrees

This is all without flaps, which will steepen angle of descent.

...kinda like being higher

This is a great idea. 3 degrees approach is more for the faster, heavier, multiengine aircraft. More power must be added for a lower angle of descent.  Always leave a way to glide a single engine home if you can.

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text:
How can I find a final approach fix (FAF)?
I have a problem understanding FAF - how can I find FAf on a precision approach without the lightning bolt/zigzag symbol. I know the Maltese cross means FAF for a non-precision approach.
According to the Jeppesen airway manual,

by the glide slope/path intercept point on precision approaches

Which means that wherever I intercept the GS, I can say that point is FAF?
I added a chart. (In case you cannot see the picture I will explain the chart) FAF (Maltese cross) is positioned at DME 5.1 and 1700ft on a 3 degree glide path.
At the moment I pass the Maltese cross at 1700 ft, the GS indicator will be below because from 5.1DME on a 3 degree glide path, altitude will be about 1620ft so I need to descend at a steeper rate to intercept the GS. Then I will intercept the GS after FAF of a non-precision approach. In this case the FAF for the precision approach is positioned after the Maltese cross?
Is the FAF of aprecision approach not fixed at a specific position?
Until now, I have regarded the Maltese cross as the FAF for precision approach because there was no lightning bolt symbol.
Please correct my misunderstanding...

This char is ILS / LOC Y RWY 19. Should i fllow stepdown or just follow glide slope? If i follow gs i will be lower that the minimum altitude 1700 at DME 5.1. IS it okay?or this stepdown profile view is for only LOC approach?

The step down fixes relate on to the LOC approach. After FAP (see my answer below) there are no such thing as step down fixes in precision approaches.

Wow thank you sir!! Freeman your grammar correction to my question is wonderful. Because i am a south korean pilot, my English is not that good. I learnt something from you. busdriver you are my saviour. I was so curious. you solved my my misconception. Sincerely thank you guys

Related

There is no Final Approach Fix (FAF) in ILS approach. There is Final Approach Point, which is indeed defined as a point where glide path intercepts the initial approach altitude.
Because the said location is arbitrary and depends on the temperature and glide can be intercepted from other altitudes or even when the AC is in a glide, there is separate point during the final approach usually around 4-5 NM from the threshold where the correct glide path and altimeter setting can be verified. This is indicated by a marker or these days more often as a DME distance.

Downvote for incorrect information. The term Final Approach Point applies only to non precision approaches. This question is in regards to precision approaches. See the Pilot/Controller Glossary: FINAL APPROACH POINT− The point, applicable only to a nonprecision approach with no depicted FAF (such as an on airport VOR), where the aircraft is established inbound on the final approach course from the procedure turn and where the final approach descent may be commenced. The FAP serves as the FAF and identifies the beginning of the final approach segment

The information offered in this answer might be correct for ICAO guidance that does not use the term FAF. However, this answer is apparently asked within the context of FAA given the reference to the lighting bolt depictions on FAA NACO charts and the reference to the FAF for precision approaches which is apparently unique to the US.

@JWalters Just FYI - ICAO does use the term FAF. FAF for non-precision / FAP for precision. The wikipedia page, and references therein, are quite good at describing the FAF/FAP situation: https://en.wikipedia.org/wiki/Final_approach#Final_Approach_Fix_%28FAF%29_and_Final_Approach_Point_%28FAP%29

For precision approaches, the Final Approach Fix (FAF) is defined as one of three points:

A lightning bolt symbol on FAA government approach plates
The (published) glide slope/path intercept point on Jeppesen approach. The glide slope/path symbol depiction starts at the FAF on these plates.
Or, it is the resultant actual point of the glideslope/path intercept when ATC directs a lower-than-published glideslope/path intercept altitude

Since FAA government (NACO) charts answer your question with the depiction of the lightning bolt symbol, your question applies primarily to Jeppesen charts (other chart vendors perhaps as well). Jeppesen charts include the glide slope intercept altitude in the briefing strip near the top of the plate. So, the FAF for precision approaches is the location at which glideslope intercept is to occur when at the lower of either the published or ATC directed altitude.
See the following excerpt from the FAA's Pilot/Controller Glossary:

FINAL APPROACH FIX− The fix from which the final approach (IFR) to an airport is executed and which identifies the beginning of the final approach segment. It is designated on Government charts by the Maltese Cross symbol for nonprecision approaches and the lightning bolt symbol for precision approaches; or when ATC directs a lower-than-published glideslope/path intercept altitude, it is the resultant actual point of the glideslope/path intercept.

See the following excerpt from Jeppesen's Airway Manual:

FINAL APPROACH FIX (FAF) — The fix from which the final approach (IFR) to an airport is executed and which identifies the beginning of the final approach segment. It is designated in the profile view of Jeppesen Terminal charts by the Maltese Cross symbol for non-precision approaches and by the glide slope/path intercept point on precision approaches. The glide slope/path symbol starts at the FAF. When ATC directs a lower-than-published Glide Slope/Path Intercept Altitude, it is the resultant actual point of the glide slope/path intercept.

Perfect sir! Thank for a specific answer


text:
Why do the 737-100's JT8Ds, and no others, have suck-in doors?
Of the various use cases of the Pratt & Whitney JT8D (the most-produced low-bypass turbofan in history, and the second-most-produced turbofan of any description1), those installed on the 737-100 appear to use a set of auxiliary suck-in doors, similar to those so familiar from the earlier JT3D:

(Image by Steve Fitzgerald at Airliners.net, via Fæ at Wikimedia Commons, modified by Fæ and Marc Lacoste at Wikimedia Commons.)
The always-useful 737 Technical Site confirms that these are, indeed, suck-in doors:

History
The original choice of powerplant was the Pratt & Whitney JT8D-1, but before the first order had been finalised the JT8D-7 was used for commonality with the current 727. The -7 was flat rated to develop the same thrust (14,000lb.st) at higher ambient temperatures than the -1 and became the standard powerplant for the -100. By the end of the -200 production the JT8D-17R was up to 17,400lb.st. thrust.
Auxiliary inlet doors were fitted to early JT8D's [sic] around the nose cowl. These were spring loaded and opened automatically whenever the pressure differential between inlet and external static pressures was high, ie slow speed, high thrust conditions (takeoff) to give additional engine air and closed again as airspeed increased causing inlet static pressure to rise.

In contrast, the JT8Ds installed on other types of aircraft, so far as I can tell, do not have suck-in doors:

DC-9

(Image by Cory W. Watts at flickr, via Josve05a at Wikimedia Commons.)

727

(Image by Pablo Andrés Ortega Chávez at flickr, via Wikimedia Commons.)

737-200

(Image by Andre Gustavo Stumpf Filho at flickr, via Wikimedia Commons.)

Caravelle 10

(Image by duch.seb at Wikimedia Commons.)

Mercure

(Image by Michel Gilliand at Airliners.net, via Fæ [again] at Wikimedia Commons, modified by Fæ at Wikimedia Commons.)

Why did the JT8D need suck-in doors on the 737-100, and not on any of the many other aircraft it was attached to?

1: Behind only the General Electric/SNECMA CFM56 high-bypass turbofan, used on (among many, many other aircraft) the 737-300 through -900.

Could be an after thought design change due to insufficient take off thrust found late in the project.

@user3528438: But the Caravelle 10B, which uses the same type and number of engines as the 737-100, and has a significantly higher MTOW (123,500 lbs., versus the 737-100's 110,000 lbs.), would be expected to need this extra thrust more than the 737-100... and, yet, the Caravelle 10B's JT8D-7s don't require suck-in doors, whereas the 737-100's JT8D-7s do.

Perhaps different aerodynamics due to wing mounting vs tail mounting?  All the shown examples other than the 737-100 are tails (but I definitely don't know that's constant...)

@ljwobker: coughcough 737-200 coughcough Mercure coughcough

SWAG here: Was the -100 certified for high & hot or short-field operations that the others weren't certified for? This may have been enabled by the suck-in doors allowing it to generate additional thrust. (Was it rated at higher thrust in the -100 than in other installations?) OK, not so much a SWAG as just a WAG...


text:
Why are some cardiac conditions disqualifying even if asymptomatic and corrected?
The FAA's website, in its list of medical conditions disqualifying for a would-be pilot, includes a number of cardiac conditions and procedures that would not intuitively seem, on their own, to warrant keeping someone on the ground, and, yet, automatically disqualify the applicant (even if they are completely asymptomatic or the condition has been corrected) from receiving a standard-issue medical certificate, requiring them to beg the FAA for a special-issuance certificate ([italicised brackets] indicate my additions):

[...]

Cardiac valve replacement [even if far in the past, with no history of symptoms or complications, and even if it completely and permanently corrected the precipitating condition]

Coronary heart disease that has been treated [even if completely resolved by said treatment] ...

...

Heart replacement [even with no history of complications]

Myocardial infarction [even if far in the past and devoid of complications or any recurrence]

Permanent cardiac pacemaker [even if causing no complications and completely resolving the underlying pacemaker-necessitating condition]

[...]

Even if some of these conditions have the potential to be associated with other, potentially-impairing conditions (such as cardiac arrhythmiae, heart failure, or heart transplant rejection), those associated conditions, if present, would be perfectly visible in their own right, without the need for using the conditions in the aboveexcerpted list as proxies.  In addition, some of the above procedures (such as valve replacement, pacemaker implantation, and some types of coronary-artery-disease interventions) are curative, or functionally-curative, procedures, and, yet, automatically disqualify their recipients from receiving a standard-issue medical certificate.
Why is this?

Heart disease? Inflammatory bowel disease is also disqualifying...

@Ron Sorry I misread a key phrase in that link, deleting comment ;)

All the conditions listed carry an increased risk of sudden cardiovascular events such as stroke, heart attack, and sudden cardiac arrest that aren't predictable and come with no forewarning.

Basics :  Why did the event happen? Will it happen again?
Curative care is fine, but what about the possibility of the same, or similar, events happening tomorrow/next month/ad astra?
The FAA medical standards are for the protection of everyone other than the pilot.
I am the proud owner of 6 cardiac stents. But it has become impossible to maintain a Special Issuance Medical as I aged.


text:
Airspeed Calibration alternate static source, what is this for?
I found a 'Airspeed Calibration Alternate Static Source' Figure in C172R POH.

There are three kinds of Figure,
1. Heater off, Vents and Windows Closed
2. Heater On, Vents Open and Windows Closed
3. Windows Open.
What are those figures for?

Your question would be improved by including a picture of the figure and any other context, such as where in the POH the information is found.

This table is included because of the fact that the Alternate Static Port on 172s is inside the cabin. Thus, changes in cabin pressure (even really small ones) can have an impact on the static pressure that the system is using and hence on the indicated airspeed.
The things the table mentions like windows and heat vents all influence the pressure in the cabin, and hence the airspeed. In reality, if you have to use the alt static port you aren't going to be pulling out the POH to correct the speed as it is likely very similar.


text:
Is there any FAA Regulation who may wash a private aircraft such as Cessna Skyhawk or Citation?
Should it be mandatory to hire a mechanic? or someone else with any kind of FAA license? or could anyone wash one?

Related

Any yahoo can wash a plane...even a pilot.
The only regulation of which I am aware concerning washes involves maintenance.  A maintainer must clean the aircraft in order to determine servicability of a component.  The regulation does not specify who must do the cleaning, however.  I doubt a FSDO (in the US) would read that as "A&P must clean it."

Any yahoo can wash it, but not any yahoo should wash it.

@RonBeyer, XL Airways Germany flight 888T is even better example as that accident was contributed by the washing technique itself rather than just failure to remove covers installed for it.

@JanHudec Another very good example, yes. At least in the 888T case they couldn't know during preflight, the 603 crew should have caught that in the walk around.

All good points but those are both airliners, not "private planes."  Common damage typically involves broken or bent antennas, use of windex on windows, and use of corrosive chemicals (like regular Sumple Green) to clean oil and grease.

I agree with Ron.  As far as regulations are concerned the onus falls on the maintenance personnel and pilots to ensure that a plane is still airworthy after being washed.

What about the cleaning required at annual, which shall be done by the IA?

That reg does not specify the extent to which the airplane must be cleaned, only that the plane must be clean enough for the IA to assess airworthiness.  My IA indicated that he may clear a small area of grease to assess the condition of a questionable grease fitting, for example, but is not going to clean the whole plane.

There is no regulation on who can wash a plane. You'll probably find that quite a few planes (at least of those used for instruction) are in fact washed by student pilots.


text:
What prevents the use of auxiliary radar installations to allow radar control and MSAW protection in areas that would otherwise be masked by terrain?
Both primary1 and secondary2 radar, while extremely useful (nay, indispensable) for modern aviation and air traffic control, are limited to seeing only aircraft in their direct line of sight; if there is something solid, such as a mountain, between an aircraft and the local radar installation, the aircraft will be invisible to radar.
This means that:

The aircraft masked by terrain will not show up on the controllers’ radarscopes, forcing them to rely on manual position and altitude reports from the pilots (and, thus, indirectly increasing the pilots’ workload as well), assuming that such reports are even available from the pilots (since, if the ATC facility’s radiocommunications transceivers are in the same, or almost the same, location as the radars [which is frequently the case], the terrain responsible for blocking radar transmissions from reaching the aircraft will generally also block VHF voice communications between the aircraft and ATC).
The various automatic protections provided to aircraft under radar coverage will be unavailable; these include MSAW (Minimum Safe Altitude Warning), which alerts the controllers to aircraft in danger of colliding with the ground, and conflict alert, which alerts the controllers to aircraft in danger of colliding with each other.

The latter of these two effects has contributed to at least one accident (as always, my emphasis unless noted otherwise):

1.18.1.3 Minimum Safe Altitude Warning (MSAW)
MSAW is a computer program to warn a controller when an airplane descends or will descend below a predetermined altitude. The MSAW at BDL was programmed to provide an alarm if the aircraft’s Mode C transponder transmitted two signals when the airplane was at or below 1,050 feet msl. However, if the radar does not pick up the aircraft’s mode C transponder signal, the program cannot function. The BDL approach control radar system produced an MSAW alarm for flight 1572 at 0055:39. The radar tracking data showed that when this alarm was produced, the aircraft was at 800 feet msl and the aircraft had already struck the trees. FAA personnel stated that under normal circumstances, the MSAW should have produced an audible alarm at that time in the tower cab, and a visual alarm should have occurred on the radar display and on the DBRITE [bright radar indicator tower equipment] in the radar room and tower cab.
Radar tracking data showed no radar "hits" from flight 1572’s mode C transponder between 0055:23 and 0055:32, and also none between 0055:05 and 0055:23. The radar antenna produces returns about every 4.5 seconds. FAA personnel reported that the reason for the absence of these hits was the shielding of the airplane from the radar by the ridge line. FAA technicians later explained that if the radar could not "paint" the airplane, the MSAW computer program could not warn the controller that the airplane was at an unsafe altitude.
According to FAA equipment design personnel, if a steady stream of Mode C information had been available to the computer, the MSAW alarm would have sounded as soon as the aircraft descended past 1,100 feet msl. They indicated that on final approach, a standardized set of MSAW parameters is used, not taking into account obstacles such as the ridge. BDL FAA personnel said that in an attempt to improve radar coverage prior to the accident, they had changed or optimized the tilt on the radar antenna, but that the ridge still obstructed radar coverage. [NTSB AAR-96/05, pages 53-54 (pages 61-62 of the PDF file of the report); section heading bolded in original.]
[...]
2.7.3 MSAW (Minimum Safe Altitude Warning)
MSAW is a computer program to warn a controller when an airplane descends or will descend below a predetermined altitude. If the radar does not receive a signal from a target, the program cannot function. The MSAW at BDL was set to alarm if the aircraft transmitted two mode C returns at or below 1,050 feet msl (30 feet below the MDA for the runway 15 VOR approach). There was no alarm as flight 1572 descended below the MDA because the aircraft was not in radar contact at that point because of shielding by the ridge line. There was a radar return recorded at 1,300 feet (above the MSAW envelope) but because of shielding from the ridge, the aircraft was out of radar contact for three radar sweeps and was therefore not visible to the controllers. Then, a single radar return was recorded at 900 feet, followed by another radar sweep with no recording of the flight, and then two radar returns were recorded at 800 feet. The MSAW then sounded an alarm, as it should have under those conditions.35 However, this alarm sounded about 4 seconds after the airplane had struck the trees.

35Two consecutive sweeps with radar contact with an airplane are required to set off the MSAW alarm. This is the reason that the MSAW did not alarm following the single radar contact at 900 feet.

According to the FAA, because of the lack of radar coverage close to the ridge, the minimums for the VOR 15 approach would have to be raised to give MSAW protection for this approach. It is not desirable for an MSAW alarm to occur above the MDA. This would result in an MSAW false alarm sounding on every approach, making the occasional valid alarm likely to be ineffective. Because the last radar return before the airplane struck the trees was recorded at 1,300 feet, the lowest altitude at which the MSAW could be programmed to activate and be effective is 1,300 feet. Therefore, to have full MSAW coverage, the approach minimums for this approach would have to be raised from 1,080 feet msl to somewhat above 1,300 feet msl, to keep the MDA above the alarm point for the MSAW. However, an MDA this high would defeat the purpose of the instrument approach. The descent from a 1,350-foot MDA to the runway would have to start far back along the final approach course, and the ceiling and visibility minimums would be unrealistically high. The Safety Board therefore concludes that despite the lack of full MSAW coverage along the approach, the MSAW operated properly, and that because of topographical limitations of the BDL local area, it is not practical to provide full MSAW coverage. [Pages 75-76 (83-84); section heading (again) bolded in original.]

A potential solution would be to place auxiliary radars on areas of obstructively-high terrain (especially areas of high terrain that would be especially prone to having aircraft behind them, such as - for instance - large hills and ridges along airport nonprecision-approach paths), allowing radar coverage, and its associated protections, to be extended to even aircraft masked from the primary radar’s view.
Why (other than cost, which must necessarily take a backseat to improvements in aviation safety) is this not done?

1: Radar which works by bouncing radio waves off aircraft (and also anything else that happens to be in the air).
2: “Radar” which works by sending out a talk-to-me signal and listening for replies from aircraft transponders.

Cost.  Ground-based radar is expensive. Especially compared to EGPWS.

@RalphJ: Feel free to make that an answer.


text:
Why is there no instrument taxi system for low-visibility operations?
In one of the comments on this answer regarding ILS category IIIc operations (or, rather, the lack thereof), it's mentioned that

There is no [radio] guidance for taxiing except the pilot's vision.

And, in an answer to another ILS IIIc question, it is stated:

There is no provision in the ILS system to provide for an auto-taxi or runway vacate. IIIc is just zero-zero and roll-out control, not auto-vacate as the linked AvWeb article seems to suggest. Its a logical extension of the FAA definition, however auto-taxi is not part of the CAT IIIc definition or system requirements. The only requirement is to get the aircraft on the runway and stopped.
...
Right now there is no airport approved for IIIc approaches because the aircraft would just sit on the runway, it has no way of taxiing in. Until an augmentation system like GPS with WAAS or LAAS, or the "Ground-Based Augmentation System" is developed further, automatic taxi is not there.
There is no provision in the existing ILS signals that allow for an aircraft to vacate the runway.

Given that the ability to land is meaningless without the ability to taxi off the runway and to the gate (this is why, even though today's airliners are perfectly capable of IIIc landings, there are, in practice, no such landings, as no airport is equipped to taxi an aircraft in from a IIIc landing), why isn't there an "Instrument Taxiing System" to allow zero-visibility taxi?

A follow-me car may be considered a near-zero visibility taxiing guidance system. (Easy to set up and maintain)

I believe that when it was created, Cat IIIc envisaged development of a zero visibility taxi guidance system using wires embedded in the taxiways.  Never came to pass, probably because the cost and time to certify such a system, for both airports and airlines, wasn't worth the relatively rare conditions where it would benefit.
Such a system using GPS is a lot more feasible now, but still the glacial pace of the cert process means it would still take forever to implement.

So it wasn't worth it even for airports where crap weather is common?

Even if you have an airport that's fogbound all the time, you have to talk a lot of other parties, manufacturers, avionics makers, gov't authorities, etc., into spending years and hundreds of millions to certify a system for the benefit of you and a few others.  Ain't gonna happen.

Such a technology today would be IR or millimeter-wave imaging and it would be combined with low visibility landing/takeoff capabilities, so taxi would come along with it for "free". Business jets are leading the way in this capability, since they often fly to smaller airports.

Also because the cert process is somewhat easier.  Bizjets had flat panel displays long before transport category a/c did.

If I were an airline executive in charge of determining the configuration of new aircraft being ordered from a manufacturer, and one of the options was an instrument taxiing system to allow so-called zero-visibility taxi, the aggregate cost of that system (purchase, maintenance, training, fuel to carry it) would have to be very low before I would consider it. My initial thought would be to reject it out of hand, but perhaps the ability to help a taxiing pilot navigate the taxiways of an unfamiliar airport would bring me around if the only cost was additional software for existing equipment. I say this as a pilot who on his first trip into Chicago O'Hare succeeded in getting some deservedly unkind words from a ground controller when I didn't turn when I should have and necessitated the rerouting of other aircraft.
In 10 years on the 747 I only once called for a follow-me car because of low visibility, and had the taxiway been better marked or my eye level lower I might not have needed that.

So it wasn't worth it even for airports where crap weather is common?

Consider the Arcata-Eureka Airport in McKinleyville, CA. The airport was deliberately built during World War II where they could depend on it being very foggy, and in that they succeeded. While the approach and landing were often challenging, there was never any real difficulty in taxiing if you were familiar with the airport.

You are right on.  Airline management will avoid spending a single dime that doesn't generate a significant seat mile cost return, especially for an expensive system that might make only a marginal improvement in overall Schedule Completion Rate.  In the regional airline industry, where the margins are REALLY tight, when it comes to modifying an existing fleet, operators would decline any improvement that didn't pay for itself in one year (it was once about 5 years).  Unless there was an AD.

@JohnK That's not always true. Fedex has equipped many of their aircraft with EVS to allow for lower minima in low vis. That couldn't have been cheap, but was apparently worth it.

Agreed.  I am sure that Fedex strives for a Schedule Completion Rate somewhat higher than pax airlines, which may be happy with 99 - 99.5%.   I  wouldn't be surprised to see Fedex shooting for 99.8 or 99.9%, and spending money on something to get there that a regular airline wouldn't.

@JohnK: Wouldn't a passenger airline tend to be more schedule-perfectionist, not less, than a freight airline like FedEx?  Passengers tend to complain loudly if their flight is delayed or cancelled due to weather; freight doesn't.

@Sean I can't speak to current practice, but back in the 1990s there were often financial penalties if you didn't get the freight where it was supposed to be on time whereas you don't have to pay pax if they're late. While jumpseating on UPS, I remember captains nervously watching the clock, aware that the guy up in the cherry picker watching everything would log the time of their block out. At PDX it was 19:00 local for the flight I often commuted on. I was told that any time after that even 19:01 would get you some attention from management.

Normally, in the passenger airline world a "delay" is a leaving the gate more than 15 minutes late.  This is "Dispatch Interruption Rate" and the normal standard is 99%+ but airplane types with technical problems can be lower than that, down around 97 or 98%, sometimes worse.  Schedule Completion Rate is trips completed one way or another, and is always a higher number, much higher if an operator has spare aircraft available (common in the Regionals).

@Terry: Really?  I wonder why that is - as I said before, I don't really see how it makes sense for freight to be more time-critical than passengers (unless you're transporting something perishable, like caviar or weathermaps, but I would guess that the vast majority of freight is not perishable).

@Sean I flew in 3 time critical freight operations. (1) There were thousands of retired Brits in the south of Spain. We picked up their morning papers at London Stansted around 03:00 local to be flown to Valencia and Palma de Majorca. I forget the exact times we had to have them at the destination, but the papers essentially became worthless if they were more than an hour or so late and the penalties reflected that. (2) On a USPS express mail contract we couldn't land before 06:00 local at Boston because of the curfew, but contractually the mail had to be at the P.O. before 07:00 local.

@Terry: ...and the third?

@Sean (3) On a UPS contract before they had their own airline, the penalties for non-compliance schedule-wise were severe. The problem was/is that each airplane coming into the sort has hundreds (thousands?) of packages that need to be routed to many other airplanes. Delaying the sort is not acceptable. If an airplane is late, it screws up everything. In case one was, they had a fleet of Learjets they'd call out to deliver the parcels of the late airplane. Very expensive.

@Sean At risk of turning the comments into a discussion, look at my answer here for reasons why a freight flight might actually be more time-critical

I think such systems may exist already per the FAA's website:

Airport Surface Detection Equipment, Model X (ASDE-X)
ASDE-X provides more precise surface detection technology. While the ASDE-3/AMASS is based on non-cooperative sensor technology, ASDE-X integrates data from a variety of sources, including radars, transponder multilateration systems and Automatic Dependent Surveillance – Broadcast (ADS-B) to provide accurate target position and identification information and thus give controllers a more reliable view of airport operations. ASDE-X provides tower controllers a surface traffic situation display with visual and audible alerting of traffic conflicts and potential collisions. ASDE-X is installed at 35 airports in the U.S.  For more information, see the ASDE-X fact sheet on the FAA website.
Airport Surface Detection Equipment, Model 3 (ASDE-3)/Airport Movement Area Safety System(AMASS)
ASDE-3/AMASS is a radar-based system that tracks ground movements and provides an automatic visual and audio alert to controllers when it detects potential collisions on airport runways. The system is usually referred to as ASDE-3/AMASS. ASDE-3 is the radar. AMASS is the software and hardware enhancement to the ASDE-3 radar that provides automated alerts and warnings to controllers. ASDE-3/AMASS is operational at nine airports.

That's just a system that lets controllers monitor movement of ground vehicles more precisely than traditional ground radar.  No help for an aircraft that needs to be able to find its way around independently.  I suppose you could have a system where ASDE-X interfaces with an on board aircraft system, but you are still talking about a massive and expensive cert program.  GPS position can now be resolved down to centimeters so whatever system comes along will likely be a standalone GPS based system.


text:
How does landing performance differ on water vs. ice vs. paved/grass runways?
It's a follow up from How do aircraft brake when using skis?
Can someone give me data about difference between landing distance for each environment ?

Paved
Grass
Water
Snow/Ice

Any aircraft is fine, provided it's fitted with brakes used during wheels landing.
Ideal answer would be comparing the same plane fitted with different landing gear on similar wind condition/ pressure

The takeoff and landing performance on different surfaces varies with condition - for example, a wet or snowy paved runway will have different braking and rolling acceleration performance than a dry paved runway. We can make some general/broad statements, but it's important to note that the specific conditions on any given day will play a large part in aircraft performance.
That said, here are some general/broad statements:

Water (and snow on skis)
Water is the odd surface in the group: It is not a runway in the traditional sense. If you "land" an aircraft with traditional hard-surface landing gear (tires) on water it is not a landing, but rather a ditching and is covered under emergency procedures.
Landing a seaplane (either a "flying boat" hull or something with floats) on water is a different beast from a landing on land, and indeed an entire different rating on your pilot certificate. Everything you ever wanted to know about seaplanes can be found in the FAA Seaplane handbook (FAA-H-8083-23), which also covers aircraft equipped with skis for landing on snow (which is in many ways similar to landing a float-equipped airplane on water).

Pavement (Asphalt, Concrete, etc.)
Paved surfaces are the baseline standard by which "land" landings are judged.  The performance charts and tables in your POH are generally given with the assumption of a dry, paved, level runway that is free of contaminants.
Wet or Contaminated Pavement
Wet, snowy, or icy pavement primarily affects braking performance: An aircraft will not be able to stop as quickly on wet pavement as the tires may hydroplane/skid with aggressive braking. This video gives a good overview of the effects of wet pavement, and while it's primarily aimed at Part 25 Transport-category aircraft/operators the same basic considerations apply for light General Aviation aircraft.
Your aircraft performance charts may discuss operations from contaminated runways, but if they do not cover this situation some rules of thumb for landing performance on wet or contaminated pavement are:

Wet Pavement (no puddles): Multiply landing distance by 1.4
Wet Pavement (w/ puddles): Multiply landing distance by 2.3
Snow on Pavement: Multiply landing distance by 1.6
Icy Pavement: Multiply by 4.5 (expecting braking to be largely ineffective)

Similarly allowances must be made for takeoff performance (additional resistance on the tires from contamination on the runway) - The usual takeoff rules of thumb work here ("Have 70% of your takeoff speed by the time you've used 50% of the runway."), with the caveat that you need to consider braking distances in the event of an abort: Aborting halfway down a 3000 foot runway when you expect to need 1800 feet to brake to a stop would be a Bad Thing.

Grass
Grass is the traditional "soft field" surface, though well-maintained grass with good drainage on a dry day may not be all that "soft" when you land on it.
As with a contaminated runway the major difference is rolling resistance: You will stop a little faster on dry, level grass than you would on an equivalent paved field because the grass offers more resistance to the tires, and you will take longer to accelerate to takeoff speed for the same reason.
Again, your aircraft performance charts may include figures for soft field / grass field takeoffs/landings (this is often given as a percentage of the paved surface figures). If your performance charts don't include soft field / grass field data there are again some rules of thumb you can use:

Short grass: Add 10% to the takeoff roll
Long grass: Add 25% to the takeoff roll
Wet grass (Soft Field): Add 35% to the takeoff roll
Muddy field: Add 50% (or more) to the takeoff roll

Paved surface landing distances work well for grass fields, with the exception of wet grass (which can be treated as a soft-field landing on wet pavement to account for your tires skidding on the wet grass).
Gravel
Though not strictly a subset of grass, considerations for gravel runways are similar: Increased rolling resistance during takeoff (as your tires push the gravel around), and diminished braking effectiveness on landing (in particular extreme braking on gravel can lock a wheel and leave a rut, as it would on a soft grass field).
Soft field takeoff and landing distances would be appropriate to use for gravel runways.

Ice
Ice is an interesting surface: It's hard, but it has a very low coefficient of friction. On clean ice your takeoff distance will be similar to pavement, but your landing distance will be significantly increased since your wheel brakes will be largely ineffective.
As for icy pavement you can plan on a landing distance of 4.5 times your paved runway landing distance (or more), and you will likely be nosewheel steering or differential braking will have reduced effectiveness for directional control (tailwheel pilots will be at a distinct advantage here, as the rudder work they do in a normal takeoff or landing is very similar to what's required to keep the aircraft going straight on ice).
Contaminated ice (standing water, snow, etc.) impose penalties similar to contaminated pavement, with the added caveat that water on ice is an incredibly low-friction surface (to illustrate this drag your finger across an ice cube dry, then do the same with a little bit of water on the surface of the ice cube) -- the increase in landing distance required would be substantial if landing on a wet ice runway.

Unique surfaces
While the list above covers the vast majority of runways you're likely to encounter there are some "unique" surfaces out there (for example perforated steel planking which is sometimes used to construct temporary runways can become a special challenge when it rains as friction on the metal is reduced by water and mud squirting up through the perforations with certain types of underlying soil).
If operating from a "unique" surface the best resource you have is other pilots who routinely operate from that surface, or at least have some experience with it -- they can tell you what to expect under different conditions, and you can plan accordingly.

Under "unique surfaces" you might include carrier decks. Then again, the arrester cable changes the parameters a bit

What about grooved runways?  Does this change the dry runway numbers, or allow you to use dry numbers when it is wet/raining?

@TomMcW Yeah, I would consider an arresting gear landing to be an entirely different beast (the carrier deck itself on the other hand I'm not sure about - depends on the coating & available friction, but I'd imagine it's similar to pavement numbers?)

@Lnafziger This AOPA blog seems to indicate that because the grooves act to improve drainage and make the wheels less prone to hydroplaning you could use the dry numbers up to the point where the runway surface is shiny/reflective, at which point the runway is considered "wet" -- of course nothing's stopping you from using the more conservative "wet" number (or something between wet & dry) for an extra margin of safety in such a case.

The data you are looking for depends heavily on the conditions at any given time (mainly wind and temperature). You can find the data for a given airframe in its accompanying POH. For example you can find the POH for the Cessna 172 Here. The POH lists the landing distance (over a 50ft obstacle on a runway) as 1250Ft. however that can vary based on conditions. The Piper Warrior POH has some very nice performance charts in section 5 that can be used to derive such information.
Grass landings are often performed using a "soft field" maneuver which involves a gentle and often slower touch down, this will add to the landing distance in general.
Water landings can be shorter or longer depending on hull/ski design and conditions. Likewise snow/Ice landings will vary with ski design and conditions. There are people who land on ice runways with regular tires, I am not sure what the performance data is since its generally not listed in the POH. In a water scenario its generally less of a concern since there is often plenty of distance available.


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How do aircraft brake when using skis?
Planes use skis to land on ice/snow runaway.
How can the plane brake in such conditions?
Friction must be limited to allow takeoff and aerodynamic braking are not the main contributors to the deceleration on wheel landings.

Image source

They must likely don't. Many wheeled aircraft are not equipped with brakes. The snow would provide resistance. The pilot would just have to account for it when landing. It might be a different story for larger aircraft but they probably have thrust reversers or propellers that can be pitched for reverse thrust

This may be answered here, although this question is more specific so probably not a dupe, IMO

You may find this manual of interest from the FAA. The short answer is that they don't have brakes like wheeled aircraft do. With sufficient runway you don't need brakes to stop a wheeled aircraft either. The airframe often provides enough drag to stop the airplane. You are generally correct that aerodynamics are not the primary method of braking, however they can in some cases be sufficient. On top of that ski operations are often flown from a frozen lake or similar area where there may be a great deal of unobstructed distance for takeoff and landing.
Some types of skis let the wheels poke through them for both snow and hard runways. In some cases the wheels may contact the ground beneath the snow and allow for traditional braking or they may be plowing through the snow providing drag.

Incidentally ice runways have a similar situation for aircraft with normal (wheel) landing gear: You can brake, but supposedly that just results in skidding so you're better off letting aerodynamic braking slow you down & using the brakes only for the final "stopping" bit.

Full up elevator and retraction of the flaps increases aerodynamic drag and downforce in the skis, reducing the time and distance required to stop.
Seaplanes have the same issue.


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Was it possible to land a Boeing 707 with 300 feet cloud ceiling in the 70s?
In the movie Airplane! (1980), the main characters had to land a Boeing 707 in Chicago airport in low visibility. The dialog says the pilot "should be able to see the runway at 300 feet".
Given the ground equipment and flight instruments of that era, is it possible to land a Boeing 707 in such condition? For example, did they have ILS? Or did they at least have VOR-DME approach that would allow the pilot to adjust the descend rate?

ILS had been around quite a while by the 1970s. The first scheduled US passenger airliner to land using it was in 1938. See https://en.wikipedia.org/wiki/Instrument_landing_system#History

"It's an entirely different kind of flying!"

Surely you can't take the movie Airplane! seriously.

@corsiKa He can if you stop calling him Shirley.

ILS approaches were in common use in 1970 when I got my instrument rating. The normal (Cat I) ceiling minimum was 200 feet. So, yes, a 707 would have been able to land with a 300 foot cloud ceiling in the 70s.
I checked Wikipedia and and found the history paragraph below:

Tests of the ILS system began in 1929 in the United States.[14] A basic system, fully operative, was introduced in 1932 at at Berlin-Tempelhof Central Airport (Germany) named LFF or "Lorenz beam" due its inventor, the C. Lorenz AG company. The Civil Aeronautics Administration (CAA) authorized installation of the system in 1941 at six locations. The first landing of a scheduled U.S. passenger airliner using ILS was on January 26, 1938, when a Pennsylvania Central Airlines Boeing 247D flew from Washington, D.C., to Pittsburgh, Pennsylvania, and landed in a snowstorm using only the Instrument Landing System.[15] The first fully automatic landing using ILS occurred in March 1964 at Bedford Airport in UK.[16]

The CAA referred to in the quote was the forerunner of the U.S. FAA.

I knew Airplane! was technically accurate. Now about the technical accuracies of Otto the autopilot...

@Bageletas I saw the film when it first came out, but my aging brain can't call up details about Otto. However, autopilots of the time, while generally very good, were not entirely trustworthy. Check out https://www.ntsb.gov/safety/safety-recs/recletters/A92_31_35.pdf. As it happened, I flew that airplane about three weeks before the noted incident, and the autopilot started a gradual roll to the right coming out of Hong Kong in clear weather during the day. In daytime in the clear, I noticed the roll of course, disengaged the autopilot, righted the airplane, and re-engaged without incident.

@Terrycloth that was a very interesting article. A slow bank into a 95° is insane. A testimony  to the crew and the plane saving it! Also, Otto was an inflatable  doll dressed like a pilot who takes off ----gear up- before the credits roll :)


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What is the largest aircraft that has been flown inverted successfully?
What is the largest aircraft that has been flown inverted? For the purpose of the question:

Sustained inverted flight is not necessary, therefore barrel rolls and loops count
The aircraft must be undamaged after the maneuver
The maneuver must be intentional (i.e. China Airliners 006 does not count)
Simulator runs do not count. The question is not "can it possibly", but "has anyone tried successfully".

The largest I am aware of is the Boeing 707, but that was more than 50 years ago. Has anyone attempted a similar feat in a larger aircraft?

I'm sure the AN225 could roll if asked.

Allegedly, the Concorde was barrel rolled, see this video, but as far as I can tell the 707 (and the Concorde if it were true) were the largest planes to be intentionally inverted, recovered, and flown. It really depends on what you mean by "inverted" though, do you mean more than 90° of bank, or do you mean completely inverted (180° of bank)?

@RonBeyer 180° of bank.

The B-47 bomber was flown through Immelman turns - see https://www.youtube.com/watch?v=6cIgTAtj4E4

Is your question "has been" or "can be"?

A FedEx DC-10 was intentionally flown inverted by the flight crew in order to thwart a would-be hijacker. Not only did they fly inverted but they did so with grotesque wounds caused by a speargun and crashaxe. Simply an amazing story. I didn't search for it, but there is an "Aviation Disasters" type show that did an episode on it. I'm sure you can find it online.

@Machavity -- Re the deleted answer by Machavity-- the photo at the bottom-- and quite likely also the video at the top-- are of radio-controlled models. The photo appears in this thread on a model airplane website: https://www.rcgroups.com/forums/showthread.php?357904-C-5-Galaxy-at-Tucson-Fly-In

Theoretically ANY airplane can be flown inverted, if you know what you are doing with it and make sure it is loaded properly throughout the maneuver.  Boeing test pilot Tex Johnson famously rolled the 707 prototype - twice - during a demo flight for airline executives at the SeaFair hydroplane races on Lake Washington in Seattle.  He nearly got fired for the stunt but the plane was perfectly fine.

The real issue is load factor: the total load imposed upon the wings divided by the gross weight of the aircraft.  Don't exceed theses values and have the aircraft flown within the required speed range and it doesn't care whether it's erect or inverted during the process.
In general though, unless an aircraft is specifically designed for inverted flight with inverted i.e. negative G fuel and oil systems, inverted flight must be maintained with a positive load factor to prevent fuel starvation and damage to the engines.
As a side note to this, DO NOT TRY AEROBATICS IF YOU HAVE NO FORMAL AEROBATIC TRAINING AND/OR ARE ATTEMPTING TO DO SO IN AN AIRPLANE IN WHICH THEY ARE NOT APPROVED.  It's true guys like Sean Tucker have done aerobatics in a Cessna Corvalis but those are experienced airshow demonstration pilots with over 20,000 hours of logged flight time and more experience at the edge of the envelope than you can shake a stick at.  You do not have this prerequisite experience and most likely will kill yourself attempting these maneuvers.

"The real issue is load factor" It doesn't have to be really. In the case of a barrel roll (like Tex's) it can be done with 1g

That's the whole point,

... And then you edited your text. Smooth captain!

Are all airplanes capable of attaining the attitudes needed for a barrel roll, or are there some airplanes whose control surfaces aren't powerful enough?

But the question is specifically about the largest aircraft that actually has been flown inverted, not which aircraft could fly inverted.

I stand by my answer.


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How do pilots use stopway, EMAS, clearway and displaced threshold?
I noticed in Why is “clearway minus stopway” used in V1 adjustments? that a stopway and an EMAS are both indicated by yellow chevrons:

Same Opa-Locka stopway on the left, and San Diego EMAS on the right. Source: Google Maps
I believe the EMAS could somehow damage the aircraft (e.g. the nose gear). This would be acceptable as this is a last resort choice to prevent exiting the runway in an overrun, and likely more serious consequences.

EMAS in use. Source: flysfo.com
In the other question it is mentioned that a stopway mustn't damage the aircraft. So my first question was What is the difference from a regulation point of view? And how the pilot can know if this is a stopway were braking is desired, or an EMAS where thrust reversers might be hazardous.
However I thing it could be interesting to open the scope and get a more complete view, so my questions are more:

How do pilots use non regular runway portions such as clearway, stopway, EMAS, displaced threshold, and possibly more of this kind if it exists?
Is there some regulation which limits them for taking off, taxiing, or landing?

Related: Advisory Circular 150/5220-22a, Advisory Circular 150/5340-1K (Page 21, Paragraph 2.10 I can't find any regulation though on requiring an airport to mark the stopway as having an EMAS or not though. It should be apparent from the pilots point of view, since EMAS pads are pretty distinctive looking.

@RonBeyer: Thanks. From these documents I see there are also concepts of Runway Protection Zone (RPZ) and Runway Safety Area (RSA).

Wow. Interesting picture. I bet they were really happy for the presence of that EMAS.

This is a loaded question.  Every regulation in aviation seems to be written blood and the need for runway safety areas (RSA) is no exception.
RSAs are defined in AC 150/5300-13A

Runway Safety Area (RSA). A defined surface surrounding the runway prepared or suitable for reducing the risk of damage to aircraft in the event of an undershoot, overshoot, or excursion from the runway.

RSA's were developed for specific reasons and are discussed in section 307 of the AC.

In the early years of aviation, all aircraft operated from relatively unimproved airfields. As aviation developed, the alignment of takeoff and landing paths centered on a well-defined area known as a landing strip. Thereafter, the requirements of more advanced aircraft necessitated improving or paving the center portion of the landing strip. While the term “landing strip” was retained to describe the graded area surrounding and upon which the runway or improved surface was constructed, the role of the landing strip changed to that of a safety area surrounding the runway. This area had to be capable under normal (dry) conditions of supporting aircraft without causing structural damage to the aircraft or injury to their occupants. Later, the designation of the area was changed to “runway safety area” to reflect its functional role. The RSA enhances the safety of aircraft which undershoot, overrun, or veer off the runway, and it provides greater accessibility for fire-fighting and rescue equipment during such incidents.

Runway safety areas surrounding a runway is typically twice the width of the runway and 1000' longer than the runway on both ends.  The 1000' of additional length is referred to as a runway end safety area (RESA).  Objects inside the RSA must have specific function and be frangible (fall down) if hit by an aircraft)

AC 150/5300-13A Figure 3-5
Let's talk about runway end safety areas (RESA).  The 1000' feet of additional space beyond the end of each runway is now mandatory.  Every airport must have a RESA at the end of the runway.  The only exception to that rule is runways with an EMAS installed.  The 1000' is not an arbitrary number either.  Through analysis of aircraft overrun incidents from 1975 to 1987 it was determined that approximately 90% of the overruns stopped within a 1000' past the end of the runway at speeds less than 70 knots.  See AC 150/5220-22a for reference.
There are airports that cannot comply with the RESA requirement due to topography, roads, railroads, houses, etc.  In these situations, the FAA has established a concept called declared distances that will push the RESA onto the runway.  This will limit the accelerate-stop distance available (ASDA) and landing distance available (LDA) values.  Airports that cannot comply with the RESA standard are limited to a runway length which is available and suitable for preflight planning purposes.  It would be impractical for the FAA to tear up perfectly good runway.
This means pilots must reference declared distance information from the current chart supplements booklet to take advantage of runway safety protections.
Take a look at KSAN runway 09 end.

Google imagery from KSAN Airport
A 1000' RESA lands in the middle of shopping center.  In this case, the RESA is moved onto the runway.  The pilots must reference the chart supplements to determine usable lengths for takeoff and landing.  Here is the declared distances from the chart supplements booklet.  The runway length is 9400' but the ASDA and LDA values 1,121 feet shorter due to no space for a RESA at the end of the runway.

Chart supplements information for KSAN
Other parts of a RSA include a runway protection zone (RPZ).  This area extends up to 1700 feet past the end of the runway and can be as wide as 500 feet depending on the type of aircraft the runway was designed for.  A little history on RPZs

Approach protection zones were originally established to define land areas underneath aircraft approach paths in which control by the airport operator was highly desirable to prevent the creation of air navigation hazards. Subsequently, a 1952 report by the President’s Airport Commission (chaired by James Doolittle), entitled The Airport and Its Neighbors, recommended the establishment of clear areas beyond runway ends. Provision of these clear areas was not only to preclude obstructions potentially hazardous to aircraft, but also to control building construction as a protection from nuisance and hazard to people on the ground. The Department of Commerce concurred with the recommendation on the basis that this area was “primarily for the purpose of safety and convenience to people on the ground.” The FAA adopted “Clear Zones” with dimensional standards to implement the Doolittle Commission’s recommendation. Guidelines were developed recommending that clear zones be kept free of structures and any development that would create a place of public assembly.

AC 150/5300-13A Figure 3-17
Take a look at KSAN runway 9 again and you will see that the runway does not have space for a runway protection zone at the end of the runway.  A RPZ is mandatory and so the RPZ is moved onto the runway.  The takeoff runway available (TORA) is also 1,121 feet shorter than the runway for just that reason.
For takeoff performance calculations, pilots are required to ensure the airplane takes off and climbs to at least 35 feet within the TODA distance to achieve the designed safety in the RPZ.

Clearways are a special type of RPZ that will not allow any obstacles other than lights that are less than 26 inches in height.  The clearway must be at ""least 500 feet wide centered on the runway centerline and the length may not be more than 1/2 the runway length."

A clearway increases the allowable aircraft operating takeoff weight without increasing runway length.

In other words, takeoff distance available (TODA) is increased beyond the runway when a clearway is installed.

Displaced thresholds are created for four reasons that are beyond the power of the airport owner / operator.

A means for obtaining additional RSA prior to the threshold.  See
paragraph 307.
A means for obtaining additional runway object free area (ROFA) prior to the threshold.  See paragraph 309.
A means for locating the RPZ to mitigate unacceptable incompatible land uses.  See paragraph 310.
Mitigation of environmental impacts, including noise impacts.

Let me answer your questions to the best of my ability
What is the difference from a regulation point of view?
A stopway is designed to allow an aircraft to stop during an aborted takeoff.  Interestingly enough the AC 150/5300-13A does not say it is designed for runway overruns during landing or undershoots on the opposite runway.  By design it will increase the ASDA value for the runway
An EMAS system replaces a stopway and is usable for undershoots while landing on the opposite runway and overruns during both takeoff and landing and is not intended to meet the definition of a stopway.  An EMAS will not increase the ASDA value for the runway

How does the pilot know if this is a stopway where braking is desired, or an EMAS where thrust reversers might be hazardous.
The chart supplements book contains information on all EMAS systems.  Looking at the declared distances for the airport will indicate the presence of a stopway when the ASDA value is greater than the runway length.  Take a look again at KSAN and you will see a note for an EMAS off of runway 27.

Chart supplements information for KSAN
Stopways are a little harder to notice but can be spotted by noticing the ASDA value is greater than the runway length.

How do pilots use non regular runway portions such as clearway, stopway, EMAS, displaced threshold, and possibly more of this kind if it exists and is there some regulation which limits them for taking off, taxiing, or landing?
What are Runway Declared Distances?
This is the easiest question of the bunch.  Pilots are required to use the applicable declared distances for takeoff and landing performance calculations.  By design declared distances take into account all of the airport design standards such as clearway, stopway, EMAS and displaced thresholds.
Declared distances bridges the gap between runway design standards and aircraft performance.

§91.103   Preflight action.
Each pilot in command shall, before beginning a flight, become familiar with all available information concerning that flight. This information must include—
(a) For a flight under IFR or a flight not in the vicinity of an airport, weather reports and forecasts, fuel requirements, alternatives available if the planned flight cannot be completed, and any known traffic delays of which the pilot in command has been advised by ATC;
(b) For any flight, runway lengths at airports of intended use, and the following takeoff and landing distance information:
(1) For civil aircraft for which an approved Airplane or Rotorcraft Flight Manual containing takeoff and landing distance data is required, the takeoff and landing distance data contained therein; and
(2) For civil aircraft other than those specified in paragraph (b)(1) of this section, other reliable information appropriate to the aircraft, relating to aircraft performance under expected values of airport elevation and runway slope, aircraft gross weight, and wind and temperature.

The AIM has information concerning runway lengths.

4−3−6. Use of Runways/Declared Distances
4-3-6(c)(1) Declared distances for a runway represent the maximum distances available and suitable for meeting takeoff and landing distance performance requirements. These distances are determined in accordance with FAA runway design standards by adding to the physical length of paved runway any clearway or stopway and subtracting from that sum any lengths necessary to obtain the standard runway safety areas, runway object free areas, or runway protection zones. As a result of these additions and subtractions, the declared distances for a runway may be more or less than the physical length of the runway as depicted on aeronautical charts and related publications, or available in electronic navigation databases provided by either the U.S. Government or commercial companies.
4-3-6(c)(2)(c) When considering the amount of runway available for use in takeoff or landing performance calculations, the declared distances published for a runway must always be used in lieu of the runway’s physical length.
4-3-6(c)(2)(d) An aircraft is not prohibited from operating beyond a declared distance limit during the takeoff, landing, or taxi operation provided the runway surface is appropriately marked as usable runway.

AIM Figure 4-3-6
How do you use declared distances for multi-engine pilots?
How do runway declared distances affect my takeoff distance?
The short version is aircraft utilizing balance field length calculations typically provide a single distance for takeoff that must be lower than both the TORA and ASDA value.
Aircraft with unbalanced field length calculations typically provide separate performance calculations for accelerate-go and accelerate-stop. The TODA and ASDA values must be greater than the calculated accelerate-go and accelerate-stop distances, respectfully.

TL;DR version
Pilots using applicable declared distances are afforded designed runway safety area protection.  Pilots who choose not to adhere to runway declared distances risk getting outside the protections designed for the runway.

That's one of the few most detailed and clear answers I've received on the site. Thanks a lot for your time. Let me add some bonus for this very useful post.

I presumed that the italicized portion of  "While the term “landing strip” was retained to describe the graded area surrounding and upon which the runway or improved surface was constructed, the primary surrounding and upon which the runway or improved surface was constructed, the primary role of the landing strip changed to that of a safety area surrounding the runway." was a simply copy/pasta error, so I cleaned that up. Please revert if that is in the original.


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How do airlines handle their non-standard passengers for the load control process?

How are non-standard passenger weights maintained in the systems?
How they do they handle these passenger weights between check in and load control system and etc..

Airlines are responsible for weight and balance control programs. In the US, FAA AC120-27 describes how these work, and it specifically describes the treatment of special passenger groups like sports teams:

What are the standard average weights for special passenger groups that do not fit an operator's standard average weight profile?

a. Sports Teams.
(1) Actual passenger weights should be used for nonstandard weight groups (sports teams, etc.) unless average weights have been established for such groups by conducting a survey in accordance with the procedures established in Section 3 of this chapter. When such groups form only a part of the total passenger load, actual weights, or established average weights for the nonstandard group, may be used for such exception groups and average weights used for the balance of the passenger load. In such instances, a notation should be made in the load manifest indicating the number of persons in the special group and identifying the group; e.g., football squad, etc.
(2) Roster weights may be used for determining the actual passenger weight.
(3) A standard allowance of 16 pounds per person may be used to account for carry-on and personal items as provided in the operator's approved carry-on bag program.
(4) If the carry-on bags are representative of the operator's profile but do not meet the number of bags authorized per person, the operator may count bags and use a 16 pounds per bag allocation.
(5) Actual weights must be used in cases where the carry-on bags are not representative of the operator's profile.
b. Groups that are predominantly male or female should use the standard average weights for males or females provided in Table 3-1.
c. Military Groups. The Department of Defense (DOD) requires actual passenger and cargo weights be used in computing the aircraft weight and balance for all DOD charter missions. This requirement is specified in DOD Commercial Air Carrier Quality and Safety requirements (reference 32 CFR part 861, section 861.4(e)(3)(ix), as revised). FAA-approved air carrier weight and balance control programs may be used to account for carry-on/personal items for mixed loads of military and their dependents (such as channel missions). For combat-equipped troop charters, the Air Mobility Command (AMC) will provide guidance to account for the additional weight. If aircraft operators perceive that the weights provided are understated, they should seek confirmation of the actual weights and should make reasonable upward estimations and adjustments to those passenger and/or bag weights.

In other words, use actual weights or come up with an appropriate method to determine appropriate average weights for special groups.